DemoApp is an application on the iPhone you probably didn't even know you had. It allows the iphone to play a single movie over and over in a repeat loop. Eric Sadun over at TUAW has a run down on the DemoApp. Heres a sample:
Where is DemoApp located?
It's found in /Applications. You will not be able to see this application without hacking your iPhone.
How do I make my iPhone automatically play a movie?
Place an h.264-encoded movie named Demo.mov into /private/var/root. Reboot your iPhone. (Power down and then re-power on.) The iPhone automatically opens your movie and begins playing it on a loop.
How do I make it stop?
Remove the movie from /private/var/root and reboot.
For the complete lowdown on DemoApp check out Erica's post on TUAW.
